2-Deoxy hexopyranoses are present in numerous biologically active natural compounds including compactin, olivimycin, mithramycin and daunomycin. The chemical synthesis of these natural products requires the ready availability of various 2-deoxy sugars in large quantities (Corey, E. J.; Weigel, L. O.; Chamberlin, A. R.; Lipshutz, B. J. Am. Chem. Soc. 1980, 102, 1439-1441). A number of reports have appeared describing methods for the preparation of 2-deoxy sugars. Most of these methods require at least two separate steps for the preparation of the desired 2-deoxy sugar. For example, 2-deoxy pyranoses and pyranosides have been obtained from glycals by hydration or hydroalkoxylation, catalyzed by methanolic hydrogen halide (Hadfield, A. F.; Sartorelli, A. C. Carbohydr. Res. 1982, 101, 197-208) or methanesulfonic acid (Ciment, D. M.; Ferrier, R. J. J. Chem. Soc. (C) 1966); by alkoxymercuration followed by borohydride reduction (Takiura, K ; Honda, S. Carbohydr. Chem. 1972, 23, 369-377; (Takiura, K.; Honda, S. Carbohydr. Res. 1972, 21, 379-391); by treatment with hydrogen halides in acetic acid (Maki, T.; Tejima, S. Chem. Pharm. Bull. (Tokyo) 1967, 15, 1069); by halohydration or alkoxylation followed by dehalogenation (Monneret, C.; Choay, P. Carbohydr. Res. 1981, 96, 299-305); and by trialkyltin hydride reduction of acylglycopyranosyl halides (Giese, B.; Gilges, S.; Groninger, K. S. Lamberty, C.; Witzel, T. Liebigs Ann. Chem. 1988, 615-617).
The most direct method for the synthesis of 2-deoxy hexopyranoses or pyranosides would be via the acid catalyzed addition of water or alcohol to acetylated glycals. Yet, this general methodology to prepare 2-deoxy sugars has remained unworkable because the protected glycals often give rearranged products under acidic condition. To date, only one preparation based on this method has been reported: V. Bolitt et al., J. Org. Chem., 55, 5812-13, (1990). In this report Bolitt et al. describe the preparation of 2-deoxyglucopyranosides by the triphenylphosphine hydrobromide catalysed addition of alcohols to a single type of sugar, glucal compounds. This method is disadvantageous because its reported scope is limited solely to glucal compounds. Further, the catalyst, triphenylphosphine hydrobromide, is a neurologic hazard, an irritant and requires separation from crude reaction mixtures. Also, the method may not be suitable for the preparation of 2-deoxypyranoses, as water incompatible reaction solvent is used.
A more useful method for the preparation of 2-deoxyhexopyranoses would require only one step, would use commercially available non-toxic reagents and catalyst, would operate on a wide variety of sugar substrates and would provide pure product directly or with minimal purification effort. None of the above described methods possess all of the attributes of the ideal method. The object of the present method is to provide a one-step method for the preparation of 2-deoxyhexopyranoses and 2-deoxyhexopyranosides which possesses the above listed attributes.